The primary aims of this paper are to (1) clarify what is meant by an action theory perspective on the study of human development, and (2) report a series of developmental studies focusing on social cognition. In particular, it is pointed out that theories, methodologies, and empirical strategies realize an action theory perspective if human beings are assumed to be potentially reflective and to act intentionally with reference to the environment. An action theory perspective on psychological development regards development itself as actively initiated through intentional, goal-directed actions and interactions of the developing subjects themselves. Methods consistent with the perspective include a combination of systematic observations and self-confrontation interviews. Specific studies reported were undertaken in three interaction contexts to evaluate the role of thinking about action. Contexts involved action accompanying social cognition in children's traffic behavior, in referential communication between parent and child, and in trainer/trainee interaction between adults and adolescents. Concluding remarks focus on potential contributions of the redefinition of social cognition as thinking about action. (RH)